Mixture of isocyanate-terminated polyurethane prepolymers

ABSTRACT

A blend of isocyanate-terminated polyurethane prepolymers is provided. The blend consists essentially of a first crystalline prepolymer based upon polyhexamethylene adipate and a second prepolymer based upon polytetramethylene ether glycol.

This is a division of application Ser. No. 08/258,611, filed Jun. 10,1994, now U.S. Pat. No. 5,436,302, which is a continuation ofapplication Ser. No. 08/054,460, filed Apr. 27, 1993, now abandoned,which is a continuation of application Ser. No. 07/515,113, filed Apr.27, 1990, now abandoned.

FIELD OF THE INVENTION

This invention relates to mixtures of isocyanate-terminatedpolyurethane. It further relates to the use of such mixtures asadhesives, coatings and sealants.

BACKGROUND

Isocyanate-terminated, polyurethane prepolymers (sometimes referred tohereinafter as polyurethane prepolymers) are desirable in a variety ofapplications. For example, they can be used in reactive hot melturethane adhesive, coating and/or sealant systems. These hot melturethane systems are solid at room temperature, melt to a viscous liquidwhen heated to moderate temperatures (82°-121° C.), and are applied in amolten state. They then cool to a solid state to provide initial bondstrength (that is, "green strength"), and, additionally, cure on contactwith ambient moisture to provide their final bond strength.

A number of reactive urethane hot melt compositions are known. Forexample, U.S. Pat. No. 3,931,077 discloses a reactive hot meltcomposition comprising (a) a urethane prepolymer prepared from a diolselected from ethylene glycol, propylene glycol, 1,4-butanediol,1,4-butinediol (sic), polymers thereof, and polytetramethyleneglycolether (sic), (b) a thermoplastic resin of an ethylene-vinylcopolymer, an ethylene-acrylic acid copolymer, an ethylene-acrylatecopolymer, an atactic polypropylene or a poly(ethyleneterephthalate)linear polymer, and (c) a tackifier.

U.S. Pat. No. 4,352,858 discloses a modified polyurethane adhesivecomposition comprising an isocyanate-terminated prepolymer and adicarbamate ester which is compatible with the prepolymer and whichcontains two free isocyanate groups.

U.K. Patent No. 2,137,638 discloses a urethane hot melt adhesivecomposition which comprises a moisture-curable polyurethane formed froma diisocyanate, a substantially linear hydroxy polyester, and amonofunctional reactant present in an amount sufficient to react with upto 40 mole percent of the isocyanate groups of the product of theprepolymer reaction.

U.S. Pat. No. 4,585,819 discloses a polyurethane hot melt compositionwhich comprises an isocyanate prepolymer, a thermoplastic polyurethaneor polyester and/or a low molecular weight synthetic resin selected fromthe group consisting of ketone resins, hydrogenation products ofacetophenone condensation resins, and mixtures thereof.

European Patent Application Publication No. 0 340 906 discloses a hotmelt polyurethane adhesive composition which comprises a mixture of atleast two amorphous polyurethane prepolymers characterized in that eachprepolymer provides a different glass transition point to thecomposition.

U.S. patent application Ser. No. 07/201,169 discloses polyurethane hotmelt adhesives, coatings and sealant systems which employ mixtures ofisocyanate-terminated polyurethane prepolymers prepared fromhydroxy-functional polyesters. These mixtures do not, however, encompassthe mixtures of the present invention. Moreover, the mixtures of thepresent invention provide better adhesion to a variety of substrates,including certain plastic substrates, than do those of the pendingapplication.

The compositions of the invention are an improvement over these priorcompositions in that they achieve adhesion to substrates even thoughthey are 100% reactive systems. Thus, while various adjuvants can beadded to the compositions of the invention, their addition isunnecessary to the attainment of adhesion.

SUMMARY OF THE INVENTION

It has now been discovered that a blend or mixture of (a) a firstcrystalline polyurethane prepolymer based upon a polyhexamethyleneadipate and (b) a second polyurethane prepolymer based upon apolytetramethylene ether glycol, provides outstanding adhesion to avariety of surfaces including polymeric surfaces. Examples of substratesto which the compositions of the invention have adhesion includepolymers such as polystyrene, polycarbonate, polyvinyl chloride,acrylnitrile/butadiene/styrene terpolymers, polyester,polymethylmethacrylate, fiber-reinforced plastic, polymer foams,corona-treated or primed polyethylene and polypropylene, etc.; wood,paper, leather, rubber, textiles, non-woven materials, and bare andpainted metals.

While prior hot melt systems provide adhesion to a variety of surfaces,it has been discovered that the blend of the invention providesexcellent adhesion to polystyrene and polymethylmethacrylate, substratesto which prior hot melt systems have not provided adequate, if any,adhesion. It has also been discovered that the blend of the inventionprovides this adhesion when used alone or in combination with otheringredients.

In accordance with the present invention, there is provided a mixture orblend of isocyanate-terminated polyurethane prepolymers which consistessentially of

(a) from 10 to 90 parts by weight of a first polyurethane prepolymerwhich comprises the reaction product of a polyhexamethylene adipate(sometimes referred to hereinafter as PHA) having a number averagemolecular weight (sometimes referred to hereinafter as Mn) of at least2,400 with a polyisocyanate, and

(b) correspondingly from 90 to 10 parts by weight of a secondpolyurethane prepolymer which comprises the reaction product of apolytetramethylene ether glycol (sometimes referred to hereinafter asTHF) having a Mn of at least 500 with a polyisocyanate,

wherein the mixture provides an isocyanate group-to-hydroxyl group ratioof greater than 1.

As noted, the blend of the invention may be used alone or in combinationwith other ingredients. Thus, for example, one or more additionalreactive components such as one or more other isocyanate-terminatedpolyurethane prepolymers may be used in combination with the blend ofthe invention. Typically, these other reactive components may compriseup to 60 weight percent of the total composition. Preferably, theycomprise from 5 to 50 weight percent of the total composition.

Preferred compositions of the invention provide an adhesion topolystyrene (sometimes referred to hereinafter as plastic adhesionvalue) of at least 3.5 kilonewtons per meter width (kN/m width). Theplastic adhesion value is determined using a modified version of ASTM D903. The procedure for determining plastic adhesion value is set outbelow in the examples.

Preferred compositions of the invention also exhibit excellent greenstrength build-up. That is, these compositions can support a 4.5kilogram tensile load for at least 120 seconds within five minutes ofmaking a bond. Still further, preferred compositions of the inventionconsistently wet substrates to which they are applied and, when testedfor adhesion, exhibit essentially no "zip" or "chatter." Zip or chatterindicates that the adhesive did not wet at least some portions of one ofthe substrates to which it is applied. As used herein, "zip" or"chatter" refers to the property of an adhesive bond to exhibit no peelstrength over certain portions of a bonded area when tested for theplastic adhesion value according to the procedures described herein.

DETAILED DESCRIPTION OF THE INVENTION

The blends or mixtures of the present invention consist essentially offrom 10 to 90 parts by weight of the first prepolymer andcorrespondingly from 90 to 10 parts by weight of the second prepolymer.Preferably, the blends or mixtures consist essentially of from 10 to 80parts by weight of the first prepolymer and, correspondingly, from 90 to20 parts by weight of the second prepolymer. More preferably, themixtures consist essentially of from 30 to 60 parts by weight of thefirst prepolymer and, correspondingly, from 70 to 40 parts by weight ofthe second prepolymer. Preferably, the blends exhibit no zip or chatter,and exhibit a green strength build-up of, at most, 5 minutes.

The prepolymers useful herein may be prepared by techniques that arewell known in the art. For example, prepolymers suitable in theinvention may be formed by reaction of a mixture of thehydroxy-functional polymers and the polyisocyanate in a suitable vessel.Alternatively, the prepolymers may be prepared by reacting each of thehydroxy-functional polymers separately with the polyisocyanate followedby blending of the resultant prepolymers. Still further, the prepolymersmay be prepared by forming one prepolymer and subsequently forming theother prepolymer or prepolymers in the first.

Typically, the components are mixed at an elevated temperature, usingconventional mixing techniques. It is preferred to mix the componentsunder anhydrous conditions. Generally, the prepolymers are preparedwithout the use of solvents.

In any case, the isocyanate equivalents should be present in thereaction mixture in an amount greater than that of the hydroxylequivalents. The equivalent ratio of isocyanate-to-hydroxyl (sometimesreferred to hereinafter as the isocyanate index) is preferably fromabout 1.2/1 to about 10/1 and especially preferably from about 1.6/1 to2.2/1.

The first and second prepolymers are derived from a polyhexamethyleneadipate (PHA) (preferably 1,6-polyhexamethylene adipate) andpolytetramethylene ether glycol (THF), respectively. While Mn of thesematerials is at least 2,750 and 500, respectively, it is preferred thatthe Mn of each be higher. It has been discovered that the performancecharacteristics of the blend or mixture may be enhanced by increasing Mnof either or both of the materials. Thus, for example, when a PHA of Mnequal to 2,400 is employed to make the first prepolymer, a THF of Mnequal to at least 2,250 is employed to make the second prepolymer. Whenthe Mn of the PHA is increased to at least 3,000, a THF with an Mn of1,000 can be used. When Mn of the PHA is 4,500, a THF of Mn of 750 canbe employed.

It should also be noted that combinations of two or more PHAs and/or twoor more THFs may be used in the preparation of the first and secondprepolymers.

PHA typically comprises the reaction product of 1,6-hexanediol andadipic acid, while THF typically is produced by the cationicpolymerization of tetrahydrofuran. However, other monomer materials mayalso be included in the polymerization mixture so as to incorporate theminto the resultant polyol. Such modified PHAs or THFs are includedwithin the scope of materials useful in preparing the first and secondprepolymers. Examples of such other monomer materials which may be usedto modify PHA include neopentyl glycol, ethylene glycol, butanediol,succinic acid, sebacic acid, etc. An example of another monomer whichmay be used to modify THF is ethylene oxide. The exact level of "othermonomer" utilized is not critical to the invention provided it does notnegatively affect adhesion. Typically, the other monomers comprise up to50 mole percent of the polymerization mixture.

It has also been discovered that the crystallinity of the THF is notcritical to the invention. Thus, this material may be amorphous,partially crystalline, or substantially crystalline.

Examples of commercially available PHAs useful in this invention include"Lexorez" 1130-30P from Inolex Chemical Co., "Rucoflex" 105-37 from RucoPolymer Corporation, and "Formrez" 66-20 from Witco Chemical Company.

Examples of commercially available THFs useful in this invention include"Polymeg" 2000 from Q O Chemical, Inc., the "Terathane" series of THFsfrom DuPont, and "PolyTHF" from BASF Corporation.

The third polyurethane prepolymer is derived from a hydroxy-functionalpolymer other than PHA or THF. This prepolymer may be added for avariety of purposes such as adjusting the set time, green strengthbuild-up, tack, final strength, etc. of the resultant mixture. Moreover,the third prepolymer may be a single prepolymer or it may be acombination of two or more prepolymers, if desired, to achieve aspecific result.

The Mn of the hydroxy-functional polymers used to make the thirdprepolymer is not critical to the invention. Thus, a wide range of Mnhydroxy-functional polymers may be employed. Examples of usefulhydroxy-function polymers in preparing the third prepolymer includepolyester (including polylactone) polyols, polyalkylene or polyalkyleneether polyols, polyacetal polyols, polyamide polyols, polyesteramidepolyols, polythioether polyols, etc.

Examples of commercially available polyols useful in preparing the thirdprepolymer are "Dynacoll" 7380 (a polyester polyol, Mn of 3,740,hydroxyl number of 30, available from Huls America), "Dynacoll" 7130 (apolyester polyol, Mn 3,740, hydroxyl number of 30, available from HulsAmerica), and "Lexorez" 3500-30P (a polyester polyol, Mn 3,740, hydroxylnumber of 30, available from Inolex Chemical Co.).

Polyisocyanates which can be reacted with the hyrdoxy-functionalpolymers to form the prepolymers used in the instant invention may bealiphatic or aromatic. Preferably, they are aromatic diisocyanates suchas diphenylmethane-2,4'-diisocyanate and/or 4,4'-diisocyanate;tolylene-2,4-diisocyanate and -2,6-diisocyanate and mixtures thereof.Other examples include: naphthylene-1,5-diisocyanate;triphenylmethane-4,4'4"-triisocyanate; phenylene-1,3-diisocyanate and-1,4-diisocyanate; dimethyl-3,3'-biphenylene-4,4'-diisocyanate;diphenylisopropylidine-4,4'-diisocyanate; biphenylene diisocyanate;xylylene-1,3-diisocyanate and xylylene-1,4-diisocyanate.

A list of useful commercially available polyisocyanates is found in theEncyclopedia of Chemical Technology, Kirk-Othmer, 2nd Ed., Vol. 12, pp.46-47, Interscience Pub., N.Y. (1967), which is incorporated herein byreference. Especially preferable isocyanates includediphenylmethane-4,4'-diisocyanate (MDI) and its isomers and mixturesthereof.

Isocyanate-functional derivative(s) of MDI and TDI may be used, such asliquid mixtures of the isocyanate-functional derivative with meltingpoint modifiers (e.g., mixtures of MDI with polycarbodiimide adductssuch as "Isonate 143L", commercially available from Dow ChemicalCompany); small amounts of polymeric diphenylmethane diisocyanates,preferably 10% or less by weight of the total isocyanate components,(e.g., "PAPI", and the series "PAPI 20", commercially available from DowChemical Company, the "Mondur" series of isocyanates commerciallyavailable from Mobay Chemical Corp., and "Rubinate M", commerciallyavailable from ICI Chemicals, Inc.); and blocked isocyanate compoundsformed by reacting aromatic isocyanates or the above-describedisocyanate-functional derivatives with blocking agents such as ketoximesand the like. Such blocked isocyanate-functional derivatives will, forconvenience, be regarded herein as isocyanate-functional derivatives ofMDI and TDI.

It is preferred that the first and second prepolymers used in thepresent invention be somewhat incompatible with one another.

Even though the first and second prepolymers are preferablyincompatible, the resultant blend typically does not exhibit macroscopicphasing. Phasing of the blends of the prepolymers can be detected in anumber of ways. For example, blends which phase demonstrate inconsistentgreen strength build-up (i.e., good build-up sometimes and poor build-upother times) even though the same composition has been used. Moreover,blends which phase may also exhibit inconsistent plastic adhesionvalues.

In addition to the third prepolymer, other ingredients or adjuvants canbe employed with the mixtures of the invention to impart or modifyparticular characteristics to the composition. They should be added onlyat a level that does not interfere with the adhesion characteristics ofthe composition. These adjuvants may comprise up to 50 weight percent ofthe composition either individually or in combination. For example,chain-extension agents (e.g., short chain polyols such as ethyleneglycol or butanediol) fillers (e.g., carbon black; glass, ceramic, metalor plastic bubbles; metal oxides such as zinc oxide; and minerals suchas talc, clays, silica, silicates, and the like), thermoplastic resins,plasticizers, antioxidants, pigments, U.V. absorbers, adhesion promoterssuch as silanes, and the like may be included to modify set time, greenstrength, build-up, tack, flexibility, etc.

In addition, the compositions of the invention may include an effectiveamount of catalyst or reaction accelerator such as tertiary amines,metal-organic compounds, co-curatives, and the like. An effective amountof a catalyst is preferably from about 0.01 to 2 percent by weight ofthe total prepolymer weight. More preferably, the catalyst is present ata level of about 0.05 to about 0.5 percent, based on the total weight ofthe prepolymer employed.

The compositions of the invention achieve their initial, or greenstrength through crystallization, then continue to cure by exposure towater, e.g., water vapor or moisture. High humidity and heat willprovide an accelerated rate of cure while low humidity (e.g., 15% R.H.or less) will provide a slower rate of cure.

While the composition of the invention is preferably essentiallynon-phasing, some separation of the prepolymer components is acceptable.Moreover, the degree of phasing can be adjusted by varying any, orseveral, of certain factors. For example, the degree of chain extensionof the prepolymers, the molecular weight of the hydroxy-functionalpolymers employed and the choice of isocyanate all influence phaseseparation. For example, as the molecular weight of the PHA decreases,the compatability of the blend increases. Additionally, as theisocyanate index ratio decreases, the compatability of the prepolymercomponents increases. Moreover, simply varying the ratios of theprepolymer components influences their compatability. Typically, themixtures of the invention are slightly hazy to translucent. Thus, whilethey are not clear, they do allow light to pass through them when in themolten state.

The following examples are offered to aid understanding of the presentinvention and are not to be construed as limiting the scope thereof. Allparts are by weight unless otherwise stated.

General Preparation of the Isocyanate-Terminated PolyurethanePrepolymers

4,4'-Diphenylmethane diisocyanate (MDI) was added to a 600 ml, stainlesssteel reactor fitted with a gas inlet adapter and a cover having arubber gasket, gas inlet, stirrer opening and stirring rod. The MDI washeated to 100° C. and melted with efficient stirring under a nitrogenblanket. After the MDI melted, polytetramethylene ether glycol (THF) wasadded to the reactor. The mixture was stirred under nitrogen for about15 minutes. The polyhexamethylene adipate (PHA) was then added to thereactor. Stirring and heating were continued for about 15 minutes, andthen 4,4'-(Oxydi-2,1-ethanediyl) bismorpholine ("Thancat" DMDEE, TexacoChemical Co.) was added. Stirring was continued under vacuum for about 1hour. Heating at 100° C. was maintained throughout. The resultingmixture was poured into nitrogen purged metal containers and sealed. Thecontainers were stored in a dessicator.

The reaction between the MDI and each of the THF and PHA was essentiallycomplete. A minor amount of unreacted ingredients remained, typicallyless than 3 percent by weight.

EXAMPLES 1-18

A series of isocyanate-terminated polyurethane prepolymers were made asdescribed in the General Preparation. Each of the resulting compositionswas tested for plastics adhesion using a modified version of ASTM D 903.Each blend was individually extruded at 107° C. onto the center portionof a 2.5 cm wide by 10 cm long×0.3 cm thick piece of isopropanol wipedrigid polystyrene (Huntsman grade 730). Immediately, a 3.8 cm wide×28.5cm long piece of canvas was bonded to the polystyrene using a press at0.7 MPa for 10 seconds. This was sufficient pressure to force the blendto cover the entire bond area and squeeze excess composition out of theedges of the bond area. The bonded substrates were then conditioned at25° C. and 50% relative humidity for 7 days. The canvas was then trimmedto 2.5 cm width, and the resulting test coupons were tested using anInstron tensile tester at a crosshead speed of 5 cm per minute. Plasticadhesion values were measured as the average of high and low readings offour coupons. The compositions of Examples 1-4, 11, 14-15 and 17exhibited some zip. In these examples, the plastic adhesion value wasthe average of the high and low value for those portions of the bondthat did not zip.

Tables 1-3 report the measured plastic adhesion values. In these tables,the reference to all concentrations of the prepolymers are in parts byweight. All concentrations of DMD are as a percentage by weight of thetotal weight of the prepolymers.

Table 2 shows the effect of varying the Mn of the THF employed.

Table 3 shows the effect of varying the Mn of the PHA employed.

Specifically, with reference to Table 1, the data show that the blend ofthe invention (Examples 2-7 and 9-11) has dramatically improved adhesionto plastic over either the use of prepolymers prepared from apolyisocyanate and either PHA or THF alone. Compare, for example, theplastics adhesion value of Example 1 with that of Example 2. Theaddition of a mere 10% of the second prepolymer to the first prepolymerincreases the plastic adhesion value by over 68%. Likewise, comparisonof Example 7 with Example 8 shows that addition of 20% of the firstprepolymer to the second prepolymer increases the plastic adhesion valueby over 2.7 times.

Examples 3-6 and 9-10 further show that the plastic adhesion value issignificantly greater over the range of mixtures claimed.

Examples 9-10 also show that the plastic adhesion value remains higheven when the isocyanate index is increased.

The data in Table 2 show that increasing the Mn of the THF utilized doesnot negatively affect the plastic adhesion value. That is, even thelowest plastic adhesion value is significantly higher than that ofeither of Examples 1 or 8. Furthermore, these values are consistent withthose reported in Table 1 for Examples 5 and 9-10.

The data in Table 3 show that increasing the Mn of the PHA does notnegatively affect the plastic adhesion value. That is, even the lowestplastic adhesion value is significantly higher than that of either ofExamples 1 or 8. Furthermore, these values are also consistent withthose reported in Table 1 for Examples 5 and 9-10 and in Table 2.

                                      TABLE 1                                     __________________________________________________________________________                 1  2   3   4   5   6   7   8  9   10                             __________________________________________________________________________    1st Prepolymer.sup.(1)                                                                     1  0.9 0.8 0.7 0.6 0.4 0.2 0  0.6 0.6                            2nd Prepolymer.sup.(2)                                                                     0  0.1 0.2 0.3 0.4 0.6 0.8 1  0.4 0.4                            DMD.sup.(3)  0.2                                                                              0.2 0.2 0.2 0.2 0.2 0.2 0.2                                                                              0.2 0.2                            ISOCYANATE INDEX                                                                           1.78                                                                             1.73                                                                              1.68                                                                              1.64                                                                              1.6 1.54                                                                              1.49                                                                              1.45                                                                             1.8 2.0                            PLASTIC ADHESION                                                              lb/in width  18 31  45  43  44.5                                                                              32  22  8  45  42.5                           kN/m width   3.2                                                                              5.4 7.9 7.5 7.8 5.6 3.8 1.4                                                                              7.9 7.4                            Clarity      clear                                                                            slight                                                                            slight                                                                            slight                                                                            slight                                                                            slight                                                                            slight                                                                            clear                                                                            slight                                                                            slight                                         haze                                                                              haze                                                                              haze                                                                              haze                                                                              haze                                                                              haze   haze                                                                              haze                           __________________________________________________________________________     .sup.(1) Prepared from 1,6Polyhexamethylene adipate ("Lexorez" 113030P        from Inolex Chemical Co., hydroxyl number of 33, Mn of 3417).                 .sup.(2) Prepared from Polytetramethylene ether glycol ("Polymeg" 2000        from Q O Chemical, Inc., hydroxyl number of 59, Mn of 1905).                  .sup.(3) 4,4'-(Oxydi2,1-ethanediyl) bismorpholine ("Thancat" DMDEE from       Texaco Chemical Company                                                  

                  TABLE 2                                                         ______________________________________                                                11   12      13      14    15    16                                   ______________________________________                                        First                                                                         Prepolymer                                                                    (1)       0.6    0.6     0.6                                                  (2)                            0.6   0.6   0.6                                Second                                                                        Prepolymer                                                                    (3)       0.4                                                                 (4)              0.4           0.4                                            (5)                                  0.4                                      (6)                      0.4               0.4                                DMD       0.2    0.2     0.2   0.2   0.2   0.2                                ISOCYAN-  1.32   1.41    1.71  1.39  1.55  1.65                               ATE INDEX                                                                     PLASTIC                                                                       ADHESION                                                                      lb/in width                                                                             28.5   29      51.5  47.5  29.5  48                                 kN/m width                                                                              5      5.1     9     8.3   5.2   8.4                                Clarity   clear  slight  slight                                                                              slight                                                                              slight                                                                              slight                                              haze    haze  haze  haze  haze                               ______________________________________                                         (1) Prepared from 1,6Polyhexamethylene adipate ("Lexorez" 113030P from        Inolex Chemical Co. hydroxyl number of 33, Mn of 3417).                       (2) Prepared from 1,6Polyhexamethylene adipate ("Rucoflex" 10537 from Ruc     Polymer Corporation, hydroxyl number of 38, Mn of 2907).                      (3) Prepared from Polytetramethylene ether glycol ("Terathane" 650 from       DuPont, hydroxyl number of 167, Mn of 671).                                   (4) Prepared from Polytetramethylene ether glycol ("Terathane" 1000 from      DuPont, hydroxyl number of 114, Mn of 988).                                   (5) Prepared from Polytetramethylene ether glycol ("Polymeg" 2000 from Q      Chemical Inc., hydroxyl number of 59, Mn of 1905).                            (6) Prepared from Polytetramethylene ether glycol ("PolyTHF" from BASF        Corporation, hydroxyl number of 39.5, mn of 2841).                       

                  TABLE 3                                                         ______________________________________                                                          17    18                                                    ______________________________________                                        First Prepolymer                                                              (1)                 0.6                                                       (2)                         0.6                                               Second Prepolymer                                                             (3)                 0.4     0.4                                               DMD                 0.2     0.2                                               ISOCYANATE INDEX    1.55    1.69                                              PLASTIC ADHESION                                                              lb/in width         29.5    53                                                kN/m width          5.2     9.3                                               Clarity             slight  slight                                                                haze    haze                                              ______________________________________                                         (1) Prepared from 1,6Polyhexamethylene adipate ("Rucoflex" 10537 from Ruc     Polymer Corporation, hydroxyl number of 38, Mn of 2907).                      (2) Prepared from 1,6Polyhexamethylene adipate ("Formrez" 6620 from Witco     Chemical Company, hydroxyl number of 22, Mn of 5048).                         (3) Prepared from Polytetramethylene ether glycol ("Polymeg" 2000 from Q      Chemical, Inc., hydroxyl number of 59, Mn of 1905).                      

After being tested for plastic adhesion, the canvas was visuallyinspected for zip. The results of this visual inspection are reportedbelow in Table 4 where the percent non-wetted area indicates zip. Thus,the greater the percentage, the greater the zip.

                  TABLE 4                                                         ______________________________________                                            1st Prepolymer/                                                               2nd Prepolymer  MnPHA/MnTHF  Non-wetted                                   Ex  (parts by weight)                                                                             (number average)                                                                           Area (%)                                     ______________________________________                                         1  1/0             3417/1905     30%                                          2  0.9/0.1         3417/1905    50                                            3  0.8/0.2         3417/1905    25                                            4  0.7/0.3         3417/1905    14                                            5  0.6/0.4         3417/1905    0                                             6  0.4/0.6         3417/1905    0                                             7  0.2/0.8         3417/1905    0                                             8  0/1             3417/1905    0                                             9  0.6/0.4         3417/1905    0                                            10  0.6/0.4         3417/1905    0                                            11  0.6/0.4         3417/671     50                                           12  0.6/0.4         3417/988     5                                            13  0.6/0.4         3417/2841    0                                            14  0.6/0.4         2907/988     20                                           15  0.6/0.4         2907/1905    30                                           16  0.6/0.4         2907/2841    0                                            17  0.6/0.4         2907/1905    30                                           18  0.6/0.4         5048/1905    0                                            ______________________________________                                    

The data shows the great ability to reduce the percent of non-wettedarea by changing the Mn of either or both of the PHA and THF used tomake the first and second prepolymers used in the mixture. Thus, at agiven Mn for either component, increasing the Mn of the other generallyreduces the non-wetted area. Examples 14 and 15 have essentiallyequivalent non-wetted areas.

The compositions of Examples 1-18 were also tested to determine theirgreen strength build-up. This property was measured as follows. A0.5+0.05 g quantity of the composition was extruded at 107° C. onto thecenter portion (about 5 cm from each end) of a 2.5 cm wide×10 cmlong×0.8 cm thick piece of Douglas Fir. A timer was started. After 10seconds, a second piece of Fir was bonded on its center point and atright angles to the first. Firm hand pressure was used to mate thesurfaces and squeeze excess composition from the bond line. At variousintervals, a 4.5 kg tensile load was pneumatically applied to the 6.45sq cm bond area. The length of time that was required for the bond tosupport the 4.5 kg load for at least 120 seconds was then recorded asthe green strength build-up. Longer times indicate poorer green strengthbuild-up.

The results of these tests are reported in Table 6.

                  TABLE 6                                                         ______________________________________                                             1st Prepolymer/                                                               2nd Prepolymer                                                                             MnPHA/MnTHF   Green Strength                                Ex   (parts by weight)                                                                          (number average)                                                                            Build-Up (min)                                ______________________________________                                         1   1/0          3417/1905     1.3                                            2   0.9/0.1      3417/1905     1.4                                            3   0.8/0.2      3417/1905     1.4                                            4   0.7/0.3      3417/1905     1.5                                            5   0.6/0.4      3417/1905     2.1                                            6   0.4/0.6      3417/1905     3.6                                            7   0.2/0.8      3417/1905     6.1                                            8   0/1          3417/1905     >10                                            9   0.6/0.4      3417/1905     2.8                                           10   0.6/0.4      3417/1905     2.9                                           11   0.6/0.4      3417/671      6.9                                           12   0.6/0.4      3417/988      3.5                                           13   0.6/0.4      3417/2841     1.4                                           14   0.6/0.4      2907/988      5.8                                           15   0.6/0.4      2907/1905     2.4                                           16   0.6/0.4      2907/2841     1.9                                           17   0.6/0.4      2907/1905     2.4                                           18   0.6/0.4      5048/1905     1.4                                           ______________________________________                                    

This data show that increasing the Mn of the THF or the PHA alone, orincreasing the Mn of both PHA and THF at the same time, improves thegreen strength build-up of the composition. The data also show thatvarying the weight ratio of the first prepolymer to the secondprepolymer affects green strength build-up.

EXAMPLES 19-25

The blend of Example 18 was tested for adhesion to various substratesaccording to the procedure described above for determining plasticadhesion except that the type of substrate was varied. The results ofthese tests are set forth in Table 7.

                  TABLE 7                                                         ______________________________________                                                          Adhesion                                                    Ex  Substrate           lb/in width                                                                             kN/m width                                  ______________________________________                                        19  Polycarbonate (isopropanol                                                                         60+      10.5+                                           wiped)                                                                    20  Fiber reinforced plastic (methyl                                                                   60+      10.5+                                           ethyl ketone wiped)                                                       22  Abraded Polyvinylchloride                                                                         61        10.7                                        22  Acrylonitrile/Butadiene/Styrene                                                                    60+      10.5+                                           terpolymer (isopropanol wiped)                                            23  Polymethylmethacrylate                                                                            76        13.3                                            (isopropanol wiped)                                                       24  Polystyrene (isopropanol wiped)                                                                   57        10                                          25  Abraded Cold Rolled Steel                                                                         63        11                                              (isopropanol wiped)                                                       ______________________________________                                    

These bonds each exhibited 100% bonding (0% unbonded area). The "+"signifies that the canvas tore before the bond failed totally.

EXAMPLES 26-28

Compositions according to the invention were prepared which employed athird prepolymer. The general preparation was employed as set forthabove except that after the PHA had been reacted with the MDI, thepolyol employed for the third prepolymer was charged to the reactor.

The resulting compositions were then tested for plastic adhesion asdescribed in Examples 1-18. Table 9 reports the results of these tests.The references to concentrations of prepolymers are in parts by weight.The reference to DMD is in percentage by weight of the total weight ofthe prepolymers.

                  TABLE 9                                                         ______________________________________                                                      26       27     28                                              ______________________________________                                        First Prepolymer                                                              (1)             60         50                                                 (2)                               55                                          Second Prepolymer                                                             (3)             30         30     15                                          Third Prepolymer                                                              (4)             10         20                                                 (5)                               20                                          (6)                               10                                          DMD (7)         0.2        0.2    0.2                                         PLASTIC ADHESION                                                              lb/in width     67         63     47                                          kN/m width      11.9       11.2   7.5                                         ______________________________________                                         (1) Prepared from 1,6Polyhexamethylene adipate ("Formez" 6620 from Witco      Chemical Co., hydroxyl number of 38, Mn of 2907).                             (2) Prepared from 1,6Polyhexamethylene adipate ("Lexorez" 11301P from         Inolex Chemical Co., hydroxyl number of 33, Mn of 3417).                      (3) Prepared from Polytetramethylene ether glycol ("Polymeg" 2000 from Q      Chemical, Inc., hydroxyl number of 59, Mn of 1905).                           (4) Prepared from a polyester polyol ("Dynacoll" 7380 from H uls America,     hydroxyl number of 30, Mn of 3740).                                           (5) Prepared from a polyester polyol ("Lexorez" 350030P from Inolex           Chemical Co., hydroxyl number of 30, Mn of 3740).                             (6) Prepared from a polyester polyol ("Dynacoll" 7130 from H uls America,     hydroxyl number of 30, Mn of 3740).                                           (7) 4,4'-(Oxydi2,1-ethanediyl) bismorpholine ("Thancat" DMDEE from Texaco     Chemical Company).                                                       

COMPARATIVE EXAMPLE

The adhesion of the blend of Example 18 to rigid polystyrene wascompared to that of a variety of commercially available moisture curinghot melt adhesives. The adhesion test was performed as described abovefor determining plastic adhesion except that the type of compositionvaried. The results of these tests are set forth in Table 8.

                  TABLE 8                                                         ______________________________________                                                          Adhesion                                                    Composition         lb/in width                                                                             kN/m width                                      ______________________________________                                        Ex. 18              57        10                                              "JET-WELD" 3876 from 3M Co.                                                                       0         0                                               "SUPERGRIP" 9601 from Bostik-                                                                     0         0                                               Tucker GmbH                                                                   "SUPERGRIP" 9704 from Bostik-                                                                     0         0                                               Tucker GmbH                                                                   "CURATHANE" 140A from Swift                                                                       0         0                                               Adhesives                                                                     "HQR" 3450 from Henkel Corp.                                                                      0         0                                               ______________________________________                                    

We claim:
 1. A composition comprising:(a) from 10 to 90 parts by weightof a first isocyanate-terminated crystalline polyurethane prepolymerthat comprises the reaction product of a polyhexamethylene adipate (PHA)having a number average molecular weight (Mn) of at least 2,400, with apolyisocyanate, and (b) correspondingly, from 90 to 10 parts by weightof a second isocyanate-terminated polyurethane prepolymer that comprisesthe reaction product of a polytetramethylene ether glycol (THF) havingnumber average molecular weight (Mn) of at least 500 with apolyisocyanate;wherein the composition has been moisture cured.
 2. Acomposition according to claim 1 wherein said PHA has an Mn of at least2,400 and said THF has an Mn of at least 2,250.
 3. A compositionaccording to claim 1 wherein said PHA has an Mn of at least 3,000 andsaid THF has an Mn of at least 1,000.
 4. A composition according toclaim 1 wherein said PHA has an Mn of at least 4,500 and said THF has anMn of
 750. 5. A composition according to claim 1 comprising from 10 to80 parts by weight of said first prepolymer and correspondingly from 90to 20 parts by weight of said second prepolymer.
 6. A compositionaccording to claim 5 comprising from 10 to 60 parts by weight of saidfirst prepolymer and correspondingly from 90 to 40 parts by weight ofsaid second prepolymer.
 7. A hot-melt adhesive, coating and/or sealantcomposition according to claim 1 having a plastic adhesion value of atleast 3.5 kilonewtons per meter of width.
 8. A hot-melt adhesive,coating and/or sealant composition comprising:(a) from 10 to 60 parts byweight of a first isocyanate-terminated, crystalline polyurethaneprepolymer that comprises the reaction product of a polyhexamethyleneadipate (PHA) having a number average molecular weight (Mn) of at least2,400, with an aromatic polyisocyanate, and (b) correspondingly, from 90to 40 parts by weight of a second isocyanate-terminated polyurethaneprepolymer that comprises the reaction product of a polytetramethyleneether glycol (THF) having a number average molecular weight (Mn) of atleast 500 with an aromatic polyisocyanate;wherein the hot-melt adhesive,coating and/or sealant composition has been moisture cured.